This invention relates to a control apparatus for a fluid flow system, such as a gasoline flow system utilized in connection with the dispensing of the gasoline from a storage tank to a vehicle.
In the dispensing of gasoline to vehicles at service stations, the gasoline is stored in an underground storage tank and is connected to a dispensing pedestal, or the like, by means of an underground conduit system. A dispensing unit, in the form of a valve-actuated nozzle, is connected to a hose which is in registery with the underground conduit system at the pedestal.
Recently, much attention has been directed to minimizing the introduction of the gasoline vapors from the vehicle tank into the atmosphere during this filling process since the vapors pollute the atmosphere and create a hazardous environment. For example, a separate vapor return line has been provided which connects the underground storage tank to the vehicle tank so that gasoline introduced into the vehicle tank will displace the vapors and force them through the vapor recovery line to the storage tank where they are mixed with the gasoline. In these type systems, the dispensing unit contains both a dispensing nozzle and a spout for receiving the vapors, and a double hose and conduit assembly is used for accommodating the gasoline and the vapors.
However, it has been discovered that under certain circumstances during the dispensing of the gasoline, the gasoline will in fact pass directly from the dispensing nozzle in the dispensing unit to the vapor recovery spout without being dispensed into the vehicle tank. For example, if the dispensing unit is adapted to shut off when the vehicle tank is full, it has been discovered that at relatively low flow rates, such as 1 or 2 gallons per minute or less, the gasoline does not get through a porthole or the like which is normally provided in the dispensing unit to effect the shut off. Rather, the gasoline can flow from the dispensing nozzle in the dispensing unit, through the vapor recovery spout, and back into the storage tank.
Also, it has been discovered that operators of the dispensing unit, after filling at least a substantial portion of the vehicle tank, can manually reduce the gasoline flow and trip the dispensing unit in a manner so that the gasoline flows out of the dispensing nozzle of the unit and back into the vapor recovery spout.
It can be appreciated that both of these situations are highly unsatisfactory since, among other things, the customer is charged for gasoline that he does not actually receive.
Another problem that exists in the dispensing of gasoline into vehicle tanks is the fact that some operators will break the seal after the vehicle tank has been substantially filled, and "top off" the tank to ensure that a maximum amount of gasoline is sold. This breaking of the seal results in vapors from the vehicle tank venting into atmosphere during the topping off operation.